Multimode self-checking flame detector

ABSTRACT

An alarm signal is operated by a multimode self-checking circuit upon failure of such circuit, or failure of a flame being monitored by a device that is sensitive to such flame. This circuit is provided with a plurality of different drive circuits each of which is designated for a flame sensitive device, such that the flame can be monitored.

ite States Patent Horn 1 1 Aug. 8, 1972 [54] MULTIMODE SELF-CHECKING3,541 ,549 11/1970 Graves ..431/24 FLAME DETECTOR 3,463,600 8/1969Axmark .43 1 I79 Inventor: R b Horn, 1 A p d D 6121i i Richardson, Tex.75080 I Primary ExaminerJhn W1 Caldwell [22] Filed May 1971 AssistantExaminer-Robert J. Mooney [21] App1.No.: 147,565 Attorney-JohnMaier,l1let al.

Related U.S. Application Data 12, 1969, abandoned.

[57] ABSTRACT An alarm signal is operated by a multimode selfcheckingcircuit upon failure of such circuit, or failure [521 [LS CI- of a flamebeing monitored by a device that is sensi- 51 1m. 01. ..G08b 29/00 Suchflame- This Circuit is Provided with a P 58] Fieldofsear h 34fl/4lo227;431/ 16 24 rality of different drive circuits each of which is431/79 designated for a flame sensitive device, such that the flame canbe monitored.

[56] References Cited 7 10 Claims, 12 Drawlng Figures UNITED STATESPATENTS 3,541,539 11/1970 Trumble ..340/227 32 w w w w w l 22 P020 PC 1I I TDI (O) 1 POWER l f 4 I BI 11 SWI agswzl 36) 44 IIEI 46 IQI 12 12sec) RI 1 1 uv L 2 WAVE I MAIN 4 A-D FFI FFZ (Q11 GI SHAPER I AMPLIFIERCONVERTER I6I 4I I 4 13 37 1 (NF) 1s1 T02 51 I (8') 12-12 sec) (0) I 1 vI I GATING 102 our 1 *1 I c1Rc u1T a: 4 72 74 MAIN FLAME ea 1 82 I RELAYI GATING 101 J c CUIT 0 our 2 I 1R I 4 1 1 1 (R) GATING I F'TnTl (Q) CIT I54 FF3 (105%)] 62 PM OUT 3 I CIR3U i: l 151 sog 64/ 1 B4 78 I DEVICEl S ss I 86 I GATlNG 56 I 527 O s 0UT4 CIRCUIT 11 l TD3 1 4 MIN) I w B0SHUTTER L J 5 1111011 PMENTEBAUB Bum 3583372 SHEU 3 [1F 5 W FIG. 6A

MULTIMODE SELF-CHECKING FLAME DETECTOR CROSS-REFERENCE TO RELATEDAPPLICATION The present application is a continuation-in-part ofBACKGROUND OF THE INVENTION It has been proposed in the past to use glowdischarge flame sensing tubes which see the flame and receive theirfiring energy therefrom.

Radiation detector tubes of the Geiger-Muller type, or ultraviolet (UV)type, requiring a particular drive circuit for each type, have also beenproposed. A photosensitive flame monitoring circuit has also beenproposed.

None of the prior systems is entirely satisfactory in actual use, andeach type of tube sensitive to the flame being monitored required itsown particular drive circuit. For example, ultraviolet tubes of one typerequired a particular circuit; those of another type of differentcircuit; and photosensitive type tubes still another difierent circuit.Prior systems were not interchangeable, insofar as tubes of differenttypes are concerned, since each type was suitable for use only with itsown particular circuit.

SUMIVIARY OF THE INVENTION An object of this invention is to provide aflame detector system that is universally suitable for use with anyselected one of the presently available commercial tubes of differenttypes including ultraviolet tubes, as well as phototype tubes.

Another object is to provide a safe and reliable selfchecking flamedetector of improved construction.

The present invention provides a multimode selfchecking flame detectorsystem which is equally suitable for use with any type of device that issensitive to rays or waves emitted by the flame being monitored. This isaccomplished by a novel amplifier control circuit that accepts theoutput of any one of several different drive circuits provided therefor,that corresponds to the selected type of tube. Preferably a commoncircuit module, a circuit board for example, is provided with anindividual drive circuit for each of several different types of tubes,and selective switching means that can be set to transfer the output ofthe so selected tube and its own drive circuit to the input of thecommon amplifier control circuit.

The amplifier control circuit comprises means for indicating the on-offcondition of the flame, as well as means for self-checking the circuititself. The flame is viewed by the tube which operates its drive circuitin response to the condition of the flame. The checking circuitperiodically energizes a shutter to blind the tube and then checks theoutput of the amplifier circuit for the so simulated flame loss. If so,the shutter is opened, and normal operation restored. If not, an alarmindicates such malfunction.

The circuit board includes a wave shaping circuit for use with theultraviolet type tube drive circuit that is selected. In case aphototype tube is selected, its drive circuit is switched into directconnection with the amplifier control circuit, so that the wave shapingcircuit is excluded therefrom.

The system comprises self-checking means which automatically operate analarm in case of any malfunction of the amplifier control circuit, aswell as when the flame being monitored becomes extinguished.

In operation the amplifier circuit receives a flame responsive signalfrom the selected tube of the photoelectric type, or one of theultraviolet types, through its corresponding drive circuit. The outputof such amplifier circuit controls signals that indicate the on-offstate of the flame, as well as means including a solid state circuit forchecking the proper functioning of the system. The flame space is viewedby the selected tube and operates its drive circuit in response to theon off state of the flame. Such drive circuit, in turn, operates theamplifier circuit in response to the conditions thereof. The operationof the selected tube is automatically self-checked by the checkingcircuit that periodically energizes a shutter to blind the tube, andthen check the output of the amplifier circuit for the simulated flameloss. If there is no malfunction, the shutter is removed, and normaloperation restored; if not, an alarm indicates such malfunction.

The invention provides in the control circuit means for adjusting thesensitivity of the amplifier circuit to the response of the tube and,hence, the flame condition; and means for adjusting the amplifier forvarying background flame conditions which are independent of each other.This sensitivity adjustment means relates to the magnitude of responseof the amplifier circuit to the response of the selected tube. Thesensitivity is adjustable, such that for high sensitivity, the magnitudeof response of the amplifier would be greater for a given response ofthe selected tube than it would be for low sensitivity. Also means areprovided for the external selection of two independent sensitivitysettings. Another feature comprises means for background adjustmentwhich is externally programmable. This background adjustment meansrelates to the ability of the amplifier to discriminate between the onstate of the flame being monitored and the radiation present due toadjacent flame. Further provision includes Flame On and Flame Out timedelay means that are independent of each other.

The self-checlring circuit is built into the amplifier control circuit.Solid state circuitry assures reliable operation, and compactconsu'uction, as well as ease of repair. Such features and advantagesare in addition to the acceptance by the invention of a selected type ofultraviolet tube, or a phototube; which renders the system of virtuallyuniversal use, insofar as the particular type of flame sensitive devicethat is selected is concemed.

BRIEF DESCRIPTION OF THE DRAWINGS The above brief description, as wellas further objects, features and advantages of the present inventionwill be more fully appreciated by reference to the following detaileddescription of a presently preferred embodiment, when taken inconnection with the accompanying drawings.

FIG. 1 is a block diagram of a multimode selfchecking flame detectorsystem illustrative of the invention.

FIGS. 2, 3 and 4 are truth tables illustrative of the operation of theA-D converter, the flip flop and time delay, respectively.

FIG. 5 is a circuit diagram of the DC and AC power supplies and waveshaping circuit.

FIGS. 6A and 6B are circuit diagrams of two different ultraviolet tubedrive circuits.

FIG. 7 is a circuit diagram of the amplifier control circuit.

FIG. 8 is a circuit diagram of the self-checking circuit.

FIGS. 9 and 9A are diagrams of the AC switch Bydirectional thyristor andgating circuits.

FIG. 10 is a fragmentary view mainly in side elevation of the flameviewing scope.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to FIG. 1 the systemillustrated comprises four major circuits PC17, PC18, PC19 and PC20which generally correspond to the respective circuit boards or module inwhich they are container. The circuit boards per se are omitted tosimplify and reduce the drawings. The areas of the major circuits areoutlined by dotted lines.

The circuit PC20 contains one type of ultraviolet tube drive circuit 22,and another different type of ultraviolet tube drive circuit 24. Acommon wave shaper 28 is provided for both of the ultraviolet tube drivecircuits 22 and 24, being connectable to a selected one of them by meansof a two-way switch SW1 having terminals 11 and 13 connected to thecircuits 22 and 24, respectively. The proper AC voltages are provided bythe corresponding drive circuit to the ultraviolet tubes 32 and 34,respectively, connected thereto.

The wave shaper 28 takes the output from either of ultraviolet drivecircuits and converts the AC voltage to a DC current, compatible withthe input requirements of main amplifier 36 of circuit board PClS.Phototube 38 is driven by a DC voltage and the signal goes directly tothe amplifier 36 when two-way switch SW2 is set to contact terminal 37.However, when it is desired to use one of the ultraviolet tubes 32, 34,switch SW2 is set to contact terminal 39, isolating lead 26 to thephototube 38.

Circuit PC20 also contains a DC power source 21 having an AC input 23;and positive, ground and negative DC outputs 25, 27 and 29,respectively; as well as AC inputs 31 and 33, respectively, to the drivecircuits 22 and 24.

Circuit PC18 contains a main amplifier 36, and Flame On" and Flame Outtime delay circuits 40 and 41. This circuit PC18 gives an analog outputto indicate relative flame strength, and also a delayed logic output Qof flip-flop (FF2) circuit 45 which is 1 when there is a flame present,and an 0 when no flame is present. The delays when going to the l and toa 0" are independently adjustable. Accordingly, the delay when going tothe I is adjusted by a potentiometer 7-R30 of FIG. 7, and the delay whengoing to a 0" is adjusted by potentiometer 7-R27 of FIG. 7.

As shown in FIG. 7, main amplifier 36 contains background adjustmentpotentiometer 7-R19 and sensitivity adjustment potentiometer 7-Rl5 and7-R16. The analog output of the amplifier 36 is indicated by a meter 42,and fed to an A-D converter 44 the outputs of which are NF and F, ofFIG. 2. With a flame present, F=0," and with no flame present, IT/F"=0.a Such two outputs go to the S" and R" inputs of flip-flop (FF!)circuit 46, the outputs of which correspond to the truth table, FIG. 3.

Assuming the main amplifier 36 receives a signal responsive to thesighting" of a flame by the selected tube (32, 34 or 38, F would go to"0," and WF' would be I. This would make 0" and "Q" of FFl circuit 46become 0 and 1, respectively. With an 0 input to time delay (TDl)circuit 40, its output (0) would become I. The output of time delay(TD2) circuit 41 would go to 0 when time t=T i.e., T seconds after itsinput went to I." This would make the inputs to flip-flop (FF2) circuit45 become l and 0 on R and S, respectively, thereby causing the output 0of FF2 circuit 45 to go to a 1. Con sequently, TD2 circuit 41 controlsthe Flame On delay.

When the selected tube ceases to see the flame, F and FF become 1" and0, respectively; and Q and O of FFl circuit 46 become I and 0. When theinput to TD2 circuit 41 goes to 0, its output goes to 1, so that now theinputs to FF2 circuit 45 are both I and its output 0 stays at I. But theinput to TDl circuit 40 goes to l at the same time, so that after T,seconds, its output goes to 0. This puts a 0 on the R input to FF2circuit 45 which causes its input Q to go to 0." Thus, TDl circuit 40controls the Flame Out delay.

Circuit PCl7 comprises circuit means for automatically checking theproper operation of the system. The automatic checking is accomplishedby periodically energizing a shutter 48 in scope 50, FIG. 10, to blindthe flame detector tube T, and then checking that the output of theamplifier circuit 36, (FIG. 1) indicates the simulated flame loss. Ifthere is flame loss, the shutter 48 is de-energized, and normaloperation is restored. If for any reason the amplifier circuit 36 doesnot respond to the simulated flame loss, the shutter stays energized,and an alarm device is activated to indicate the malfunction.

Time delay (TD3) circuit 52 controls the frequency of the checks. Ifthere is no flame present (6 of FFl circuit 46 is 0) when TD3 circuit 52times out, it will go to 0 momentarily; but since the R input to FF3circuit 54 is also 0, the output of FF3 circuit is unknown and Q may goto l momentarily and pulse the checker solenoid 56, FIG. 10. Thishappens whenever time t=nT where n is an integer from 1 to Assuming aflame F, FIG. 10, has just been initiated, the Q output from circuitPC18 (FFl circuit 46) has just gone from 0 to l When TD3 circuit 52,FIG. 1, has timed (t=nT its output goes to 0," thereby changing thestatus of the output of FF3 circuit 52, so that Q is 1 and O is 0. The Ooutput goes to Out-4 circuit 58, which causes the checker to beenergized and also starts TD4 circuit 60.

If the output of the flame detector goes to 0 to indicate no flamebefore TD4 circuit 60 times out, then FF3 circuit 52 is reset (R is 0, Sis l and Q of FF3 circuit 52 goes back to 0: de-energizing TD4 circuit60 and the checker; and 0" of FF3 circuit 52 goes to I to start TD3circuit 52 again. Since the shutter 48, FIG. 10, is deenergized as soonas the amplifier responds to the loss of flame, the main output ofcircuit PC18, that is Q of FF2 circuit 45, does not respond becausethere is not enough time to time-out TDl circuit 40.

If, on the other hand, the detector does not pick up the loss of flame,TD4 circuit 60 times out, giving a 0 at 8 of FF4 circuit 62 (R is stilll), so the Q output FF4 circuit 62 goes to 1. This 1 goes to Out-3circuit 64 to give an unsuccessful check alarm by activating device 100,and also to multivibrator (MVl) circuit 66. This starts MVl circuit 66oscillating and this signal is used to flash a Main Flame On" lamp 101through Out-2 circuit 68, thereby providing another indication of theunsuccessful check. The signal to a Main Flame Relay coil 102 continuesundisturbed.

The circuit continues in such state until the amplifier circuit gives ano flame signal (6 of FF1 circuit 46 is 0). When this happens, FF3circuit 54 is reset as before. Q of FF3 circuit 54 going to 0 causes theoutput of TD4 circuit 60 to go to 1 so that R and 8 of FF4 circuit 62are 0 and 1, respectively; causing Q to go to 0. This stops MVl circuit66 from oscillating and also de-energizes Out-3 circuit 64 and therebythe alarm device 100.

The output circuits (Out 1-4) 70, 68, 64 and 58 are used to increase thecurrent output capability of the low power solid state circuitry toenable relatively high powered devices such as lamp 101, relay coil 102,solenoid 56 (FIG. 10) and alarm device 100 to be activated.

The circuit PC19 contains AC switching Bidirectional thyristors 74, 76,78 and 80; and gating circuits 72, 82, 84 and 86. The Bi-directionalthyristors drive the external AC operated devices, such as the checkersolenoid 56, FIG. 10. The gating circuits receive logic level signalsfrom circuit PC17 and convert them to the proper form to gate theBi-directional thyristors.

The blocks shown in FIG. 1 correspond substantially to the actualcircuitry of the flame detector, and the following description relatesto such actual circuits.

UV TUBE DRIVE CIRCUITS Circuits 22 and 24, FIG. 1, match the specificcharacteristics of each different type of UV detector tube used therein.These circuits provide the proper drive voltages for the selected tubeand also provide a pulse to the wave shaping circuit 28 each time theselected UV detector tube fires.

In FIG. 6A there is shown a drive circuit 22 for use with aunidirectional gas discharge tube 32. This tube 32 conducts only in onedirection. When voltage E across AC voltage source T1 is positive andtube 32 conducts, current flows through resistor 112, causing a voltageto appear between lines 114 and 115. Due to the action of capacitor 111in the circuit the voltage across resistor 112 is of a pulse nature.This pulse is coupled to the wave shaping circuit (FIG. 5) by leads 114and 115, (FIG. 6A) being connected to leads 108 and 109, FIG. 5,respectively. Resistor 110 serves to discharge capacitor 111 during thetime voltage E across AC voltage source T1 is negative and the UV tube32 is not conducting.

A drive circuit 24 for use with a Bi-directional gas discharge tube 34is shown in FIG. 6B. This type of tube can conduct in either direction.If the voltage across voltage source T1 is sufficiently high, positiveor negative, and UV tube 34 conducts, current will flow through resistor119. This will cause a voltage across resistor 119 with a polaritydepending on the direction of the current flow through tube 34. Thisvoltage is rectified by a diode bridge 120 and applied to the waveshaping circuit of FIG. 5 by connecting leads 121 and 122, FIG. 6B, toleads 108 and 109, FIG. 5, respectively.

WAVE SHAPING CIRCUIT The circuit 28, FIG. 5 comprises a siliconcontrolled rectifier Q1, resistors R6 through R13, capacitor C5 anddiode bridge D5.

The voltage across the rectifier O1 is a full wave rectified ACdeveloped by diode bridge D5. Whenever the rectifier O1 is fired by apulse from one of the drive circuits it draws current through resistorsR8 and R9 and capacitor C5. This charges capacitor C5. During the timewhen the rectifier O1 is not conducting, capacitor C5 discharges throughresistors R9, R8, R10 and R11, so that the magnitude of the voltageacross capacitor C5 is proportional to the period of time the rectifierO1 is conducting.

The voltage across capacitor C5 is divided down by resistors R11 and R10and then applied through resistors R12 or R12 and R13 to the input ofthe amplifier circuit 36 through leads 6], 62 and 63. Resistors R12 andR13 convert the voltage across capacitor C5 to a proportional currentwhich is the proper input to the amplifier circuit 36.

The silicon controlled rectifier (SCR) O1 is provided because thecurrent pulses produced by each tube are different and may vary with theintensity of ultraviolet light and/or other factors. But, if a pulse ispresent, it will fire such SCR Q1, which will always conduct for thewhole half cycle and the magnitude of the current it draws is fixed bythe voltage of the secondary winding of transformer T2, and the valuesof the resistors in its anode circuit. Therefore, whenever the selectedultraviolet tube fires, uniform pulses appear across capacitor C5, sothat its voltage is proportional to the number of pulses per second.

PHOTOTUBE DRIVE CIRCUI'I Phototube 38, FIG. 1, is connected in a seriescircuit from the negative terminal 29 of the power supply 21 directly tothe input of the amplifier circuit 36 through lead 26 to contact 37 ofswitch SW2.

D.C. POWER SUPPLY This circuit 21, FIG. 5, comprises a secondary winding92 of the transformer T2, diode bridge D8, resistors R14 through R16,capacitor C6 and zener diode D6 and D7. It provides DC. voltage of i1 2volts, for example, to the flame detector circuits. The output ofwinding 92 of transformer T2 is rectified by diode bridge D8. The outputof the diode bridge D8 is filtered by resistor R14 and capacitor C6. Thevoltage across capacitor C6 is then reduced by resistor R15 andregulated by zener diodes D6 and D7.

MAIN AMPLIFIER The main amplifier circuit 36 (FIG. 7) comprisessubstantially all of the circuit to the left of transistor 7-03; and isa current-to-voltage converter. The input to this circuit is a current(I in) applied to lead 104, and its output is a voltage (E out)appearing at lead 105 proportional thereto. This is represented by thefollowing formula:

E out =(I in) (7-R10) (X), where Xcan be varied from 1-26 to provide thesensitivity adjustment, by adjusting either resistance 7-Rl5 or 7-R16.This provides two independent adjustments which can be programmed orselected externally by energizing or deenergizing relay 7-RL1 byrespectively closing or opening switch 106.

The main amplifier includes an operational amplifier A1 with fieldeffect transistor 7-01 used to provide high impedance input stage.Transistor 7-02 and resistors 7-R50, 7-R48, and 7-R47 supply a constantsource current for transistor 7-01. Resistor 7-R36 and capacitor 7-C14serve as an input filter for the input signal connected to line 104.Resistors 7-R34 and 7-R35 are the load resistors for the inputtransistor 7-01. Resistors 7-R37, 7-R40 and 7-R38, 7-R41 comprise twovoltage dividers which reduce the output signal of the input stage to asuitable level for operational amplifier A1. Resistor 7-R45 and diodes7-D1 and 7-D2 serve to limit the voltage appearing on line 105. Resistor7-Rl0 and capacitor 7-Cl3 are the feedback network for the combinedamplifier and field effect input stage while resistors 7-R43, 7-R44,7-R42 and capacitors 7-C11, 7-C10 and 7-C12 serve to bias and compensatethe operational amplifier A1. Diode 7-D3 and resistor 7-R46 establish astable reference voltage for background adjustment potentiometers 7-R19and 107, the output of which are applied to the non-inverting input ofthe main amplifier through resistor 7-R39, and which is filtered bycapacitor 7-C9. Resistor 7-R18 in conjunction with sensitivitypotentiometers 7-R15 and 7-Rl6 form two voltage dividers which supplythe feedback voltage to the feedback network 7-R10 and 7-C13. Resistor7-R49 is used to drive a meter to provide a visual indication of flamecondition.

A-D CONVERTER The A-D converter circuit 44, FIG. 7, includes transistorunit 7-03 and resistors 7-R23, 7-R24 and 7-R25 connected as shown. Suchtransistor unit 7-03 is of the high gain dual type comprisingtransistors A and B connected in the differential mode. With the inputto transistor A of the transistor unit 7-03 negative, the transistor Ais cut off and its collector is high. This is the F output shown inFIGS. 1 and 2. Transistor B is on, and its collector is low (almostground). When the input to transistor A of the unit 7-03 goes positive,it turns on, its collector (F") goes low, and the collector oftransistor B (NF) goes high.

FFl CIRCUIT The FFl circuit 46, FIG. 7, includes two cross connectedNand gates 7-G1A and 7-GlC.

TDI CIRCUIT The TDl circuit 40, FIG. 7, includes resistors 7-R26, 7-R27,7-R28 and 7-R32, capacitor 7-C7, diode 7-D4 and transistor 7-04connected as shown. When the input to this circuit through resistor7-R26 goes high, capacitor 7-C7 starts to charge through resistors 7-R26and 7-R27. The gate of transistor 7-04 is biased by logic gate 7-G1B atapproximately 6.5 volts. When capacitor 7-C7 charges to the bias voltageof transistor 7-04 the transistor breaks down, discharges capacitor 7-C7through resistor 7-R28 and pulls the input to logic gate 7-G1B low.Diode 7-D4 is used to discharge capacitor 7-C7 in case the input to thetime delay goes back to zero before the time delay has timed out. Thiscauses instant reset so that the timer will always provide the fulltime.

TD2 CIRCUIT The TD2 circuit 41, FIG. 7, includes resistors 7-R29, 7-R30,7-R3l and 7-R33, capacitor 7-C8, diode 7-D5 and transistor 7-05connected as shown. The operation of this circuit is similar to thatdescribed above for TDl circuit 40.

FF2 CIRCUIT The FF2 circuit 45, FIG. 7, includes gates 7-G1B and 7-G1Dwhich are connected and operate similarly to the FFl circuit 46 asdescribed above.

FF3 CIRCUIT The FF3 circuit 54, FIG. 8, includes gates 8-G1A and 8-G1Bwhich operate as described above re: the FFl circuit 46.

TD3 CIRCUIT The TD3 circuit 52, FIG. 8, includes the components to theleft of resistor 8-R5 and capacitor 8-C3. The operation of this timedelay is substantially similar to that of TD circuit 40, except that avoltage divider comprising resistors 8-R3 and 8-R4 is used to bias thegate of transistor 8-02; and transistor 8-01 is used to amplify thecapacitance of capacitor 8-C2. The circuit is such that for similarresistances and capacitances, the de/dt in the first case will besmaller by a value of approximately l/B, B being the current gain oftransistor 8-01. Diode 8-D1 discharges capacitor 8-C2 through resistor8-R2 when transistor 8-02 breaks down. Diodes 8-D8 and 8-D9 act tocompensate for leakage in capacitor 8-C2 at elevated temperatures.

TD4 CIRCUIT The TD4 circuit 60, FIG. 8, comprises resistors 8-R6, 8-R7and 8-R8, capacitor 8-C4, diode 8-D4 and transistor 8-03 connected asshown. Operation of this circuit is similar to that to TDl circuit asset forth above.

FF4 CIRCUIT The FF4 circuit 62, FIG. 8, includes gates 8-G1C and 8-G1D,and its operation is similar to that of the FFl circuit 46.

MVl CIRCUIT The MVl circuit 66, FIG. 8, includes resistors 8-R9 through8-Rl4, capacitors 8-C5 and 8-C6, diodes 8-D5 and 8-D6, transistors 8-04and 8-05. The circuit 66 is one that is known for multivibrators, exceptthat it can operate only when the output of gate 8-G1C is high. With theoutput of gate 8-G1C low, transistor 8-05 is cutoff and its collector,the output of the MVl circuit 66 is high.

OUT 1-4 CIRCUITS OUT 1, 2, 3, 4 circuits 70, 68, 64 and 58, FIG. 1,consist essentially of Nand gates 8-G2D, 8-G2C, 8-G2B and 8-G2A,respectively, FIG. 8. Such gates are used to drive the relays 9-RL1,9-RL2, 9-RL3 and 9-RL4, FIG. 9.

GATING CIRCUITS 1,2,3,4

As shown in FIGS. 9 and 9A, such circuits comprise reed relays 9-RL1,9-RL2, 9-RL3 and 9-RL4 and diodes 9-D1, 9-D2, 9-D3 and 9-D4. Such reedrelays are operated by the outputs of the gates in FIG. 8, and supplythe gate signal for Bi-directional thyristors 9-Ql, 9-02, 9-03 and 9Q4which correspond to 74, 76, 78 and 80, FIG. 1. The Bi-directionalthyristors, in turn control the operation of device alarm 100, lamp 101,relay 102 and solenoid 56, FIG. 1, as will be clearly understood bythose skilled in the art.

SUMMARY OF ADVANTAGES To sunu'narize, the invention includes thefollowing important advantages and/or features:

1. The system will accept several commercially available ultraviolet orphototube.

2. Background and sensitivity adjustment as defined above areindependent of each other whereby a change in one has no efi'ect in theaction of the other one.

3. Independent sensitivity adjustments are externally selectable as byswitch 106, FIG. 7, which can be located some distance from the flamedetector.

4. Background adjustment is externally programmable, as by potentiometer107, FIG. 7, which also can be located some distance from the flamedetector.

5. The system is composed essentially of solid state devices includingoutputs.

6. Flame On and Flame Out time delays are independent of each other.

7. The checker circuit constitutes a component part of the system.

A latitude of modification, change and substitution is intended in theforegoing disclosure and in some instances some features of theinvention will be employed without a corresponding use of otherfeatures. Accordingly, it is appropriate that the appended claims beconstrued broadly and in a manner consistent with the spirit and scopeof the invention herein.

What is claimed is:

l. A multimode flame detector system capable of use with any selectedone of a plurality of different types of ultraviolet and photosensitivetubes that are sensitive to rays emitted by a flame to be monitoredthereby comprising means for indicating when such flame is in ancondition,

a control circuit containing an amplifier circuit for operating the outcondition indicating means,

a plurality of individual drive circuits corresponding to such tubetypes, each being capable of delivering flame condition signals suitablefor reception by said amplifier circuit when energized and connectedthereto;

means for connecting the selected type of tube exclusively to the drivecircuit corresponding thereto, and

means for delivering only the output of the so connected drive circuitto the input of said amplifier of the control circuit;

whereby the system functions equally well with any selected type ofultraviolet and photosensitive tube that is suitable for monitoring suchflame.

2. A multimode flame detector system as defined by claim 1, in which aunitary circuit module contains said drive circuits and tube connectionmeans.

3. A multimode flame detector system as defined by claim 2, in whichsaid module consists of a circuit board containing two different UV tubedrive circuits and a phototube drive circuit,

a wave shaping circuit for said UV tube drive circuits,

means for connecting a selected one of said UV tube drive circuits tosaid wave shaping circuit, and

means for connecting the output of either said wave shaping circuit, orsaid phototube drive circuit, to the input of said amplifier circuit.

4. A multimode flame detector system as defined by claim 3, in whichsaid control circuit includes self checking circuit means comprisingmeans acting to periodically blind the tube to such flame whenperiodically energized to check the output of the circuit for the sosimulated flame loss,

means acting to remove such blind when the circuit is functioningnormally, and

means acting to operate said means to indicate a circuit malfunctionwhen that occurs.

5. A system as defined by claim 4, including means for adjusting thesensitivity of the amplifier circuit to the response of the tube and,hence, the flame condition, and

means for adjusting the amplifier for varying background flameconditions independently of such sensitivity adjustment.

6. A system as defined by claim 5, including means for preselecting suchsensitivity adjustment for at least two settings, and

external means for selecting a desired one of said settings.

7. A system as defined by claim 5, including means for externallyprogramming such background.

8. A system as defined by claim 5, including independent Flame On andFlame Out time delay circuits.

9. A system as defined by claim 5, in which solid state componentsincluding outputs are used substantially throughout the system.

10. A system as defined by claim 5 in which said checking circuit is acomponent of the amplifier-control circuit.

1. A multimode flame detector system capable of use with any selectedone of a plurality of different types of ultraviolet and photosensitivetubes that are sensitive to rays emitted by a flame to be monitoredthereby comprising means for indicating when such flame is in an''''out'''' condition, a control circuit containing an amplifier circuitfor operating the ''''out'''' condition indicating means, a plurality ofindividual drive circuits corresponding to such tube types, each beingcapable of delivering flame condition signals suitable for reception bysaid amplifier circuit when energized and connected thereto; means forconnecting the selected type of tube exclusively to the drive circuitcorresponding thereto, and means for delivering only the output of theso connected drive circuit to the input of said amplifier of the controlcircuit; whereby the system functions equally well with any selectedtype of ultraviolet and photosensitive tube that is suitable formonitoring such flame.
 2. A multimode flame detector system as definedby claim 1, in which a unitary circuit module contains said drivecircuits and tube connection means.
 3. A multimode flame detector systemas defined by claim 2, in which said module consists of a circuit boardcontaining two different UV tube drive circuits and a phototube drivecircuit, a wave shaping circuit for said UV tube drive circuits, meansfor connecting a selected one of said UV tube drive circuits to saidwave shaping circuit, and means for connecting the outpuT of either saidwave shaping circuit, or said phototube drive circuit, to the input ofsaid amplifier circuit.
 4. A multimode flame detector system as definedby claim 3, in which said control circuit includes self checking circuitmeans comprising means acting to periodically blind the tube to suchflame when periodically energized to check the output of the circuit forthe so simulated flame loss, means acting to remove such blind when thecircuit is functioning normally, and means acting to operate said meansto indicate a circuit malfunction when that occurs.
 5. A system asdefined by claim 4, including means for adjusting the sensitivity of theamplifier circuit to the response of the tube and, hence, the flamecondition, and means for adjusting the amplifier for varying backgroundflame conditions independently of such sensitivity adjustment.
 6. Asystem as defined by claim 5, including means for preselecting suchsensitivity adjustment for at least two settings, and external means forselecting a desired one of said settings.
 7. A system as defined byclaim 5, including means for externally programming such background. 8.A system as defined by claim 5, including independent ''''Flame On''''and ''''Flame Out'''' time delay circuits.
 9. A system as defined byclaim 5, in which solid state components including outputs are usedsubstantially throughout the system.
 10. A system as defined by claim 5in which said checking circuit is a component of the amplifier-controlcircuit.